Since the early days of the pandemic, some researchers have advocated a fast way to determine whether a COVID-19 vaccine works: Intentionally attempt to infect vaccinated volunteers with the virus, SARS-CoV-2. Ethicists and vaccine scientists alike raised red flags, and the discussion has remained mostly theoretical. But now two key elements are taking shape: a large corps of volunteers willing to take part in a “human challenge” trial, and the well-understood lab-grown virus strains needed for the studies.
Challenge studies are always ethically challenging, but the circumstances here a little unusual. Generally, challenge studies follow thorough lab testing and then monitoring across the earlier Phases, but we’ve arrived at this point very quickly. Also usually, there will be an established treatment that can be used if the experimental agent doesn’t work. We don’t have such a treatment. We know infection can be fatal and there are indications there can be long term lung and brain damage. Yet the stakes can’t be more compelling. The death toll every day is truly awful and billions crying out for vaccine and treatment.
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Researchers use human challenges to test vaccines for other diseases, including cholera and malaria, but in those experiments, proven drugs can help “rescue” study participants if the vaccine doesn’t work and they become seriously ill. In a June report on COVID-19 vaccine challenges, an advisory group to the World Health Organization (WHO) was split over whether they should take place in the absence of a rescue treatment. The group was also evenly divided on whether human challenges would truly speed the vaccine effort, given that efficacy trials using participants at risk of natural infection have already begun. Still, the report offered guidelines for these trials, suggesting they should recruit volunteers between ages 18 and 25 and require them to remain in “high-level isolation units” during the study so they don’t infect others.
